1. Field of the Invention
The present invention relates to low drag, collapsible or foldable fan systems. In particular, the present invention relates to a fan having foldable blades adapted to be positioned in ducting conduit of a ram air induction system on a vehicle such as an aircraft, spacecraft, ocean vessel, land conveyance vehicle or the like.
2. Background of the Invention
In many vehicles, airflow is often utilized as a cooling medium to chill coolants that are circulated through a heat exchanger. In particular, many vehicles utilize ram air induction systems to capture air as a function of the movement of the vehicle, and to channel the air through ducting conduits which lead to a heat exchanger. If the ram air induction is designed properly, when the vehicle is in motion, sufficient airflow is provided to the heat exchanger by the ram action of the air as the vehicle travels through an air medium.
An inherent characteristic and disadvantage with ram air induction systems is that optimal airflow, which is essential for optimal cooling, is usually directly proportional to vehicle speed or velocity. Therefore, when the vehicle is not moving, minimal airflow is delivered to the heat exchanger which significantly reduces the cooling efficiency of the heat exchanger.
While many vehicle cooling requirements are easily satisfied by ram air induction systems, other vehicles require “ground cooling”. For instance, when a vehicle is powered-up and yet still stationary, many systems of a vehicle may be creating heat which require cooling. If the vehicle is supporting a mission in which no travel is required, ground support equipment (GSE) may be connected to or tapped into the cooling lines of the vehicle to provide chilled coolant. However, if the vehicle mission ultimately requires travel, there is inherently is a transitory period either before and/or after the mission (e.g., prior or after take-off for an aircraft), or even during a mission, in which the vehicle is not in motion or is not traveling fast enough to receive the benefits of ram air. Furthermore, in this transitory period GSE is not viable to support ground cooling since the vehicle ultimately has to travel to accomplish the mission.
To overcome this disadvantage, an auxiliary fan may be placed internally within the ducting conduit of the ram air induction system to provide enough airflow to the heat exchanger for proper cooling operation. In this scenario, the fan is usually turned off when sufficient ram inducted airflow is delivered to the heat exchanger as indicated by instrumentation which shows proper cooling. However, this approach has it own disadvantage. In particular, since the fan blades are static while the motor is deactivated, a pressure drop that is detrimental to optimal heat exchanger design and/or operation is created between the backside of the fan blades and entrance side of the heat exchanger.
It is proposed that a low drag fan assembly having foldable fan blades be utilized as the auxiliary fan positioned within the ducting conduit of the ram air induction system to overcome these known disadvantages. With this arrangement, the fan blades may be folded or collapsed back while the vehicle is in motion and receiving sufficient ram air. As a result, the airflow obstruction created by the static fan blades is substantially reduced.
A review of the prior art reveals that there are no known apparatuses or systems currently available which are designed to provide sufficient airflow to a heat exchanger positioned within a ducting conduit of a ram air induction system. For example, U.S. Pat. No. 1,728,768 to O'Connor teaches a ventilation device capable of permitting either forced or natural flow of air through a conduit. However, even though O'Connor teaches positioning a fan with folding fan blades within a conduit, the O'Connor system is not a ram air induction system for a vehicle which utilizes a heat exchanger. In other words, the O'Connor is specifically designed to handle either fan forced or natural flowing air, not ram air created from movement of the vehicle.
Other prior art examples include the use of folding fan blades in turbines, turbo fans, or turboprop propulsion systems (see U.S. Pat. No. 3,957,229 to Davis, U.S. Pat. No. 4,394,109 to Ritchie, and U.S. Pat. No. 4,936,526 to Gries), however, these prior art references only teach the concept of folding fans. Furthermore, the aforementioned prior art is related to propulsion systems, not cooling systems. Further, other prior art references teach foldable fan blades (see U.S. Pat. No. 4,776,761 to Diaz and U.S. Pat. No. 6,161,994 to Lang), however, these references are not related to ram air induction systems.
It would be desirable to provide a low drag fan assembly which may be utilized as the auxiliary fan positioned within the ducting conduit of a ram air induction system. In particular, it would be beneficial to provide a system in which the fan blades may be folded back or collapsed while the vehicle is in motion and receiving sufficient ram air, such that the low pressure pocket created by static fan blades may be substantially reduced.